RAM UPGRADE

2010 iMacs have user upgrade able RAM, however Apple has never made a 25” iMac! It is either a 21.5” or 27”. Only use Crucial.com or Macsales.com RAM , iMacs need quality RAM and both vendors offer high quality reasonably priced products.

Maximum Memory 16 GB

Memory Slots 4 - 204-pin PC3-10600 (1333 MHz) DDR3 SO-DIMM

well, there are 21,5 and 27" iMacs - which one is it?

You’re quite welcome.

See the memory install video here:

https://eshop.macsales.com/shop/memory/iMac/2010/DDR3_21.5_27